Circadian Rhythm of Helobdella robusta: a Study on daily activity and timeless gene

Most of life forms have circadian clocks, but the details with respect to the mechanisms and the extents of influence vary between species. In this study, I studied the circadian rhythm in the behavior and gene expression of the leeches, Helobdella robusta. The leeches belong to Lophotrochozoa, one of the three major groups of bilaterally symmetric animals. This study focuses on behavioral observation first and also documents the temporal expression profile of a ‘circadian clock’ gene – Timeless homolog – in leech. In the behavior observation section, I found that the leeches are more active and having more walking distance during the night than during the day. In the summary, I found that the leeches have the circadian clock in the body. In the gene expression study, I found that the expression level of Timeless homolog is more during the night than during the day. However, the roles of Timeless homolog and other candidate genes in regulation of circadian behavior of the leeches are still unknown. More researches are needed for understanding the molecular and neural mechanism underlying the circadian behavior rhythm in the leech.